Drum-type wood chippers of the kind typically used to chip tree limbs and other wood debris include a housing having an internal chamber in which a chipper drum is supported for driven rotation. The drum carries a plurality of cutting knives spaced about its perimeter which, when wood debris is fed into the chamber, reduce the limbs and such to chips. The chips are discharged through an outlet in the chamber and transported by their momentum along a discharge chute for collection, typically in a chamber or bin, such as that provided on a towing vehicle used to transport the chipper.
As the type of wood and size of the chips can vary, it is not uncommon for some of the chips to be too light such that they have insufficient momentum to travel the length of the discharge chute and collect in the chamber. One proposed solution to the problem has been to add fan blades to the side of the drum in order to generate a flow of air in the chipping chamber to help carry the chips along. The flow of air, however, is difficult to control and in some cases an undesirable backflow develops wherein dust and light debris is discharged through the material inlet.
Another proposal has been to equip such chippers with a fan external to the housing that is driven off the drum shaft and is coupled by a hose to the discharge chute for creating an air flow in the chute downstream of the outlet which acts to draw and carry the chips along and into the collection bin. While such external fan devices are effective at entraining the chips, there is not always room enough on the chipper apparatus to accommodate the mounting of the external fan assembly. Further, the necessity for an additional air hose from the fan to the discharge chamber detracts from the appearance of the chipper apparatus, is prone to damage, and adds to the maintenance and cost of the apparatus.